1. Field of the Invention
The present invention relates to a semiconductor device and a method of fabricating the same.
2. Description of the Background Art
A semiconductor device comprising an interlayer dielectric film is known in general. In such a semiconductor device comprising the interlayer dielectric film, a structure in which a low dielectric constant film is employed as the interlayer dielectric film has been considered in order to avoid delay of information transfer (RC delay) in a wire portion resulting from a parasitic capacitance of a wire formed on or under the interlayer dielectric film. The material of the low dielectric constant film includes a low dielectric constant film having a dielectric constant of around 2.7 such as an organic polymer material represented by polyaryl ether (PAE), or an SiOC material represented by hydrogen silsesquioxane (HSQ) or methyl silsesquioxane (MSQ) in addition to fluorinated silicate glass (FSG) having a dielectric constant of about 3.5 which has been relatively actually employed in general. In recent years, low dielectric constant films like a porous silica film having a dielectric constant of around 2.2 by making these porous have been attempted to be applied.
The aforementioned film having holes made porous, however, has a low mechanical strength, and hence it is required to improve a mechanical strength of portions other than the holes. A method for improving the mechanical strength of the porous silica film by performing a hardening treatment with ultraviolet light is proposed in Japanese Patent Laying-Open No. 2003-268356.
In the method proposed in Japanese Patent Laying-Open No. 2003-268356, however, ultraviolet light permeates through the porous silica film when the hardening treatment with ultraviolet light is performed, whereby in a case where a metal film such as Cu exists in a lower layer of the porous silica film, oxidation of the metal film is facilitated due to reaction of ultraviolet light and air. Thus, the resistance of the metal film is disadvantageously increased. In a case where the organic film such as a SiOC film exists in the lower layer of the porous silica film, desorption of hydrophobic groups such as —CH3 groups contained in the organic film with ultraviolet light permeating through the porous silica film increases hygroscopicity, whereby dielectric constant of the organic film is disadvantageously increased.